Traditionally, a telecommunication apparatus were designed to work in one communication mode, which was assigned a particular frequency range in which only signals belonging to that communication mode was present. This has evolved to telecommunication apparatuses able to work within more than one communication mode, where each communication mode has its predetermined and well-known frequency range. However, a multi-mode telecommunication apparatus that is to connect to a telecommunication system where a plurality of communication modes is present may face a signal environment where it is frequency bands that have operation for several communication modes. Here, the number of combinations of carrier frequencies and communication modes in a desired or possible frequency range for operation becomes large, which makes initial synchronization time long and power consuming.
According to one prior art approach of dealing with this, which is disclosed in US 2007/0091785 A1, the search is based on information in a history list. The history list includes frequency ranges and bandwidths that have been used before.
Another approach is disclosed in US 2006/0009216 A1, in which a scan list is modified to remove all non-current-mode systems and sequentially scanning a highest priority channel on the modified scan list. If a communication device has recently found service on a particular system in a first mode, the communication device will only search for systems that are associated with that first mode.
A problem still to be solved is thus to cope with first time synchronization, or when the signal environment has changed significantly, e.g. switching on the communication apparatus in a new geographical situation.